OCR A-level Biology PracticalS Test Exam Questions And
Answers Verified 100% Correct
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment)
- ANSWER 1. cut equal size pieces of beetroot and rinse them to remove any pigment
released during cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures for the same length
of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into covet for the colorimeter
*make sure to calibrate the colorimeter with a blank first
6. measure the absorbance rate of each liquid
7. the more absorbance (less light passing through) the more permeable the membrane
was
* more transmission = less permeable the membrane
variables to control:
-temperature
-ethanol concentration
-No excess dye on cut sections of beetroot (rinse off)
-swirl liquid before putting in the cuvette for the
-time
-beetroot (age, same plant, same part) -SA
and/or mass of beetroot used.
** remember
judging colors by eye is not as good as using colorimeter because the results are
judged subjectively or by using a colorimeter
Practical 9: Determining glucose concentration - ANSWER Method 1: Test strips and
then compare to a chart
Practical 10: Using a potometer (Factors affecting transpiration rates) - ANSWER 1. cut
a shoot underwater to prevent air from entering the xylem (interferes with the column of
, wtaer travelling up the xylem) cut a slant to increase the surface area available for water
uptake.
2. Assemble the potometer in the water and insert the shoot underwater, so no air can
enter the water.
3. remove the apparatus from the water but keep the end of the capillary tube
submerged in a beaker of water.
4. check the apparatus is watertight (vaselline etc)
5 dry the leaves to allow time for shoots to acclimatize
6. remove the end of the capillary tube from the beaker of water until one air bubble
had formed, put the capillary tube back into the water.
7. record the starting position of the air bubble along the ruler.
8. start the stopwatch and record the distance moved by the bubble per unit time
9. rate of air bubble movement is the rate of transpiration
10. all other conditions must be kept constant. only one change should be variable.
independent variables:
- wind speed
- use a fan
-humidity (plastic bag over the plant)
-light intensity ( lamp distance away from plant)
-temperature
variables to control
water uptake
no all water is ivolved in transpiration
some may be used to maintain tugidity or some use in photosynthesis
Practical 11: The effect of antibiotics on bacterial growth - ANSWER 1. dip discs in
antibiotics
2. place on bacterial culture
3. measure inhibition zone
Practical 12: Dilution plating to determine the density of microbes in liquid culture.
**biotechnology and bacterial culture. (Factors affecting the growth of microorganisms) -
ANSWER 1. supplies a sample of bacteria broth.
2 make dilutions if necessary
3. using a sterile pipette add a set volume of sample onto agar plate
4. spread the brith across entire surface of the agar using a sterile spreader 5. put
the lid on the agar plate and tape it shut repeat steps 3-5 for six plates control :
uncultured agar plate
leave all plates for the same amount of time
Answers Verified 100% Correct
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment)
- ANSWER 1. cut equal size pieces of beetroot and rinse them to remove any pigment
released during cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures for the same length
of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into covet for the colorimeter
*make sure to calibrate the colorimeter with a blank first
6. measure the absorbance rate of each liquid
7. the more absorbance (less light passing through) the more permeable the membrane
was
* more transmission = less permeable the membrane
variables to control:
-temperature
-ethanol concentration
-No excess dye on cut sections of beetroot (rinse off)
-swirl liquid before putting in the cuvette for the
-time
-beetroot (age, same plant, same part) -SA
and/or mass of beetroot used.
** remember
judging colors by eye is not as good as using colorimeter because the results are
judged subjectively or by using a colorimeter
Practical 9: Determining glucose concentration - ANSWER Method 1: Test strips and
then compare to a chart
Practical 10: Using a potometer (Factors affecting transpiration rates) - ANSWER 1. cut
a shoot underwater to prevent air from entering the xylem (interferes with the column of
, wtaer travelling up the xylem) cut a slant to increase the surface area available for water
uptake.
2. Assemble the potometer in the water and insert the shoot underwater, so no air can
enter the water.
3. remove the apparatus from the water but keep the end of the capillary tube
submerged in a beaker of water.
4. check the apparatus is watertight (vaselline etc)
5 dry the leaves to allow time for shoots to acclimatize
6. remove the end of the capillary tube from the beaker of water until one air bubble
had formed, put the capillary tube back into the water.
7. record the starting position of the air bubble along the ruler.
8. start the stopwatch and record the distance moved by the bubble per unit time
9. rate of air bubble movement is the rate of transpiration
10. all other conditions must be kept constant. only one change should be variable.
independent variables:
- wind speed
- use a fan
-humidity (plastic bag over the plant)
-light intensity ( lamp distance away from plant)
-temperature
variables to control
water uptake
no all water is ivolved in transpiration
some may be used to maintain tugidity or some use in photosynthesis
Practical 11: The effect of antibiotics on bacterial growth - ANSWER 1. dip discs in
antibiotics
2. place on bacterial culture
3. measure inhibition zone
Practical 12: Dilution plating to determine the density of microbes in liquid culture.
**biotechnology and bacterial culture. (Factors affecting the growth of microorganisms) -
ANSWER 1. supplies a sample of bacteria broth.
2 make dilutions if necessary
3. using a sterile pipette add a set volume of sample onto agar plate
4. spread the brith across entire surface of the agar using a sterile spreader 5. put
the lid on the agar plate and tape it shut repeat steps 3-5 for six plates control :
uncultured agar plate
leave all plates for the same amount of time
